The present invention relates to a switchable hydraulic mount.
From the prior art, switchable hydraulic mounts, also referred to as hydrobearings, are known, in which the decoupling action of a decoupling membrane can be varied by closing an opening of a decoupling chamber by means of a linear actuator. The decoupling membrane is arranged between the fluid-filled work chamber and the air-filled decoupling chamber and fluidically separates these chambers. When the opening is closed, the air volume enclosed in the decoupling chamber acts as an air spring. The spring stiffness depends on the size of the decoupling membrane and on the volume of the decoupling chamber among other factors. When the opening of the decoupling chamber is closed, the spring stiffness of the enclosed air volume is high, i.e., during the deflection of the decoupling membrane, the spring stiffness of the enclosed volume counteracts the deflection. Conversely, by opening the decoupling chamber, the spring stiffness is reduced, since the decoupling chamber then does not represent a closed-off, fluid-tight volume but is instead connected via channels to other large volumes or to the environment, and, when the membrane is deflected, a fluid exchange occurs. As a consequence, the spring stiffness decreases significantly under the membrane, and thus the transfer of vibrations also decreases at certain excitation frequencies and excitation amplitudes (decoupling).
Another consequence of the decoupling is that the work chamber is decoupled from the collection chamber, that is to say substantially no fluid exchange occurs between the work chamber and the collection chamber via the damping channel, and thus no hydraulic damping occurs either. When the decoupling chamber is opened, the hydraulic mount therefore exhibits a low stiffness and a low hydraulic damping for certain excitation frequencies and excitation amplitudes.
On the other hand, when the opening of the decoupling chamber is closed by means of the linear actuator, air can no longer escape from the decoupling chamber into the environment, so that the possible deflection of the decoupling membrane is reduced due to the spring stiffness of the air in the decoupling chamber. Depending on the deflection of the decoupling membrane, a high pressure or low pressure which is opposite to the deflection is generated. Thereby, the decoupling action of the decoupling membrane is reduced, and, at the specified excitation frequencies and excitation amplitudes, the work fluid flows back and forth substantially between the work chamber and the collection chamber via the damping channel, so that, when the decoupling chamber is closed, the hydraulic mount exhibits a high stiffness and a high damping. Thus, in engine mounts, the stiffness and damping behavior, for example, can be varied in a targeted manner in a standing, idling vehicle by switching the linear actuator. Above-described switchable hydraulic mounts are disclosed in EP 1 443 240 A1 or WO 01/63138 A1, for example.
However, in the conventional switchable hydraulic mounts, the problem is that high actuation forces of the linear actuator are necessary for the closing of the opening of the decoupling chamber, in order to close or keep closed the decoupling chamber against the pressures applied. Due to the high actuation forces, large and expensive linear actuators are used for the switchable hydraulic mounts. Furthermore, in conventional switchable hydraulic mounts, the opening and closing noises due to these high actuation forces can also be quite considerable and disturbing.